US2454847A - Mold, mold charging, and molding process - Google Patents

Description

Nov. 30, 11.948. A, SLAQK, JR 2,454,847

MOLD, MOLD GHARGING, AND MOLDING PROCESS Filed April'zg, 1 944 :s sheets-sheet 1 Nov. 30, 1948. FQ A, SLACK, JR r 2,454,847

MOLD, MOLD CHARGINC', AND MOLDING lPROCESS Fild April 29,1944 l s sheets-sheer 3 5910.1 l k\ 11HI Patented Nov. 30, 1948 lJNl'l'ED STATES PATENT einen rricr;

MOLD, MOLD CHARGING, AND MOLDING PROCESS Application April 29, 1944, Serial No. 533,298 25 Claims. (c1. ils-'341) This invention relates to molds, mold charging and molding processes, pertaining particularly to the production of articles such as artificial teeth having at least two physically or visually contrasting portions.

Although molding is an art of great antiquity yet it has taken on added impetus and importance pursuant to the development of .thermo-setting and thermo-plastic compounds. These materials have led through various forms of molding to the present economical and high speed forms of molding, represented by compression, extrusion, injection and transfer molding and combinations of or developments of same, which have effected radical changes in molding techniques. It is noteworthy however, .that all .such improved forms of molding have been available only for the use of a single homogeneous charge for the production of a single homogeneous mass having the same uniform internal as well as superficial characteristics and the same uniform visual aspect as the result of a physical and visual uniform structure throughout the molded mass. So far as known all such high speed molding has concerned itself solely with imparting shape and dimensions to a uniform molded mass. When the article becomes more complicated and has one portion of an accurately predetermined shape or area having one visual aspect or physical structure, while another portion of the entity has another accurately predetermined shapeor area having a different contrasting visual aspect or physical structure, such as is presented, for purely illustrative example by an articial tooth, a problem is presented which the known modern molding methods cannot solve. In short,gwhenever two or more different batches or lots of moldable material are to be joined in carefully predetermined'relative proportions and accurately predetermined relative shapes into an integral molded unit, none of the presently known high speed molds, or mold charging or molding processes are either available for or capable of such molding. This is true so far asr known, whether the difference between the illustrative two lots, batches or charges of material comprises a mere subtle difference of shading or hue, or a difference between the degrees of brightness or saturation or shading of the same hue, or whether it is a difference in texture, density, physical characteristics, a difference in materials themselves, or even a dilierence between the initial physical states of the different lots or batches such as to whether they are respectively fluids, or solids, or mixtures thereof.

Artificial teeth as previously developed were made of clays, different lots of which were provided with varying proportions or amounts of modifying materials such as opaciers, pigments and the like, establishing a plurality of at least two relatively different lots', batches orcharges of material, which respectively required very accurate relative shaping and proportioning in the molds to establish the necessary visual effects in the nished tooth. However, despite years of effort, no really efficient molds, or charging or molding processes Iwere developed to facilitate such molding. Certainly nothing was developed in the art of porcelain tooth manufacture that could be successfully used in the production of plastic artificial teeth, although the problems in ultimate visual aspect of the completed artificial teeth, regardless of the materials from which they are made, are practically identical. Thus in any articial tooth, in a simple illustrative form thereof, it is essential to have an incisal tip'of relatively translucent material which is also prolonged across the entire or almost the entire labial surface of the tooth, which in a given tooth requires usually one material of known characteristics to be handled. It is also essential to have at least a second material of known-characteristics so as to represent enamel, extending partially toward but spaced from the incisal tip While overlying and backing up the translucent material of the labial surface and usually forming part at least of the lingual tooth surface and this is or may be accompanied by still a third material of known characteristics merging into but visually contrasted with the enamel and forming the body and rootl of the tooth. Sometimes further additional intermediate charges of material are used to assist blending but in every case of teethfor mounting in a denture there are at least two different charges. In the formation of porcelain teeth the various clays and mixtures were respectively required to be moistened into a plastic or malleable mass which was relatively form-retaining, which could then be shaped and proportioned and initially nred to produce a bisque, appreciably larger than the ultimate porcelain artificial tooth completed by a second prolonged high temperature ring. Such molding methods for porcelain teeth involved the use of a multi-part mold having complemental recesses, which, when joined, formed the individual closed mold cavities in whichthe bisques were formed.

In this illustrative form of prior art practices, commercial success was always qualied or conshaped it as best he could to both s0 dispose it the mold recess as to cover at least -part of the labial surface of the ultimate tooth, While .also building it above the level of the thickness as great as he believed would just per- 4 reduce the costs of molds; to provide a mold such that successive charges of dry powder can be properly disposed in the mold cavities in any desired degree of mutual blending; to reduce the weight of molds for molding plastic articles; to reduce the labor involved in molding plastic articles; V,to provide a moldingtechnique by which at will and selectively two visually contrasting colors or material can be associated in a molded article either with a sharp line of separation between contiguous charges cr with a subtle blending solthatone merges into the other withrecess in a mit the incisal portion to be engagedand 'n'ally shaped by the complemental mold recess-of` .the

other mold part when subsequently assembled'. This initial charging and shaping of the 4iirst malleable mass Was then followed by, at least, a second estimate as to volume by'whichthe oper ator removed a charge from asecond batchand forced vit into the openrecessto overlie the 'maL teren for the labial surface While also building it i up in thickness so as to enable the second charge to be flriallyh'aped bythe complemental mold recess when the mold cavity was nally completed and closed. Similar estimates and shaping were required for additional charges, if any, disposed in the incomplete mold cavity, all as preliminary to the initial firing of the assembled mold land contents to form `the clay bisque. As such highly skilled labor as is essential for such techniques and practices is scarce andexpensive, .so also the percentage of discards resulting from such purely manual skill is high, the production rate is low, the deterioration of molds is high because 'of abrasion,y with an ultimate high cost yof the porcelain Yteeth when completed.v Note that by this molding process it is necessary to charge ,the entire mold cavity fby successive stages .of charging one half thereof only and shaping the charges successively in the lower half to .properly ll the complete mold cavity when it is subsequently completed by juxtaposing the complementalmold recesses in the upper and lower mold yhalves to form the complete closed mold cavities.

It is probable that intimate knowledge-of the art of porcelain tooth manufacture has interfered with the development of efficient molds,.and charging and molding processes for the manu-V facture of plastic artiiicial teeth'. At anygrateso far as known none such have yet been yevolved and present plastic tooth manufacture has cone tinued to revolve about mcdications .of porcelain tooth molding techniques, with'consequent unsatisfactory, expensive and variable 'products which all fall far short of the perfection that is attainable from and is achieved by the invention herein'.

It is among the objects ofthis invention; to provide improvements in molds; to provide improvements in the art of charging molds; vto pro; vide improvements in the art of molding; toprovide a molded plastic tooth of denseness and lif`elike coloring and shadings and with each in uniformity with others of a series; to simulate a natural vital tooth in an artificial tooth made of a plastic; to provide molds and a charging and molding technique by which a series, of plastic articles can be -molded each possessed of atleast two predetermined physically or visually contrasting portions;` to cheapen `the costs of molding; to

vo'ut such sharp line; to reduce the amount oi Waste hitherto attaching to molds and molding `processes;- :to provide improvements in molds and charging: and molding processes by which wear on the mold parts is for all practical purposes precluded, vwith va vconsequent avoidance of the previously necessary frequent replacement of the mold parts; to provide a molding and charging process by which an iniinite range of colors and shades can be imparted to a molded article; to 'provide a mold with a charging reservoir equidistant from all mold cavities; to provide a mold which vcan vbe charged by gravity; to provide a mold which can be charged centrifugally; to provide a mold which can be charged as a resultant of both gravity and centrifugal force; to provide a molding process forplastic articles in which a plurality-of mold cavities are subjected to identical molding pressures to secure uniformity of the products; to provide a method and means for forming a succession .of plastic teeth of uniform perfection y"to provideimprovements in molds and charging'and molding methods which lend themselves to automaticactuation and functioning; to providemolds for plastic teeth of respectively different sizes the heating cycle of which is predeter minedly the same; toprovide molds oi generally cylindrical shape for uniformity of charging and molding the mold" cavities; to eliminate moving parts inmolds; to provide molds for vforming a plurality of plastic larticles which are readily stripped from thejmold; 'to' provide arnold and chargingV and molding processes by which a molded object may have only two contrasting portions and by which the object may also have practically an innite number of contrasting portions according to the preference ofthe operator.; to provide improve'ments in ymolds and charging .and molding processes by which articles cfa single uniform visual aspect can be v produced Wtheiiiciency and economy; and many yother .objects .and advantages Will become more apparent as the description pro-- ceeds,

In carrying ,out-the .invention in a preferred but purely illustrative om a centrally `charged two-piece Inold fis provided in which the mold cavities formed of, complementa] surfaces in the lower,` and upper .mold pieces are substantially radially.,dis'p sed `irran annular series substantially concentric relative to a hopper -or reservoir channels into the respective mold cavities until there is a solid column of powder extending from the incisal tip end of the respective mold cavities lirough the remainder of the mold cavities, the sprue channels, said into the hopper or reservoir. The powder passes from the delivery tube and reservoir into and is shaped and Iproportioned properly in the mold cavities either gravitationally or under the influence of centrifugal force, or a combination of both. The first powder delivered through the tube in charging is that, for instance which is to form the incisal tip'of the molded tooth. After a metered amount has been directed into each mold cavity, the flowing stream of powder is changed from incisal tip material, to enamel material, for instance. This change may be either abrupt, as by stopping one flowing charging stream before beginning the next, or it may be very gradual indeed by overlapping supplies causing some portion of the flowing stream entering the hopper to be comprised of portions from both the incisal tip material and the enamel. In the usual course, with a iiowing stream of abruptly changing charges, there may be enough change of direction and mutual tumbling and intermixture of the parts of two different charges as to cause very satisfactory blending of the respective spectral distributions of the two predeterminedly contrasting parts, or powders of various shades, or color combinations may be .A

preliminarily prepared by preblending before simple feeding.

In molding, the completely charged assembled mold, with the powdered plastic in the continuous column from one end of each mold cavity to the filled central hopper, is then heated for a predetermined interval to change the consistency of the plastic powder into a column of more or less viscous mutually adherent particles capable of being forced into a solid whole under suitable pressure. The heated mold itself is then subjected to transverse pressure to resist separation of and minimize without necessarily completely precluding flash between the mold pieces during the maintenance of which pressure a piston is forced into the heated mass in the hopper, placing the mass and thus the column of materials in the sprue channels and mold cavities under such pressure as to unify and solidify the entire column without disturbing in any way the blending attaching to the mode of charging just recited, then while maintaining the pressure, the entire mold is permitted to cool, after which the mold pieces separated, then the molded mass is stripped from whichever mold piece it may adhere to after separation of the mold, 4the molded teeth are cut from the sprues, and the finished teeth are finally treated to remove all flash, sprue and parting line indications.

In the accompanying drawings forming part of this description,

Fig. lvrepresents a plan of a purely illustrative form of lower mold piece or mold half, according to this invention.

Fig. 2 represents a bottom or reflected plan of the upper half or mold piece complemental to that of Fig. 1, in a purely illustrative form.

Fig. 3 represents a transverse section through the two cooperating complemental mold pieces of Figs. l and 2, in a separated position prior to assembly Ato denne the complete mold cavities, sprue channels and hopper of the preferred form of the invention.

Fig. 4 represents a transverse section through the joined mold portions or pieces of Figs. 1 and 2, with a purely illustrative plastic-discharging tube in one operative position in the charging hopper of the assembled mold, with the mold unit shown, illustrativelypas mounted on a turntable to develop centrifugal force rto distribute the initial powdered plastic in the respective mold cavities. l

Fig. 5 represents a similar section with a material of the second of the series of charges discharged from the tube and illustratively disposed centrifugally, in the mold cavities in compacted relation to the initial lot or batch of powder.

Fig. 6 represents a section of the assembled mold relatively completely lled with compacted plastic powder and being disposed on a heated plate in order to cause an initial plasticising or partial polymerization of the plastic in the mold cavities and central charging hopper.

Fig. 'Z represents a similar section through the same assembled mold pieces and plastic contents with a pressure plate and working piston to force and hold the mold pieces together to reduce flash, prior to and during piston actuation.

Fig.` 8 represents a similar section to that of Fig. 7, with the working piston forced into the mass in the hopper of the mold, to exert compression force evenly throughout the plastic cole umn and to insure that the cavities are evenly and densely lled with the rigidied and solidified plastic material.

Fig. 9 represents an illustrative product of the molding process shown in perspective 'showing the small amount of waste associated with the products.

Fig. 10 represents va transverse section through a modiiied form -of mold adapted for gravity charging. f

Fig..1l represents a plan of the operating face of the upper mold pie-ce of Fig. 1G.

. Fig. 12 represents a fragmentary enlarged secA tion on an exaggerated scale through the portions of the mold pieces Adefining a mold cavity and with the latter filled with three illustrative shades or charges of overlapping and -contrasting materials, comprising the important divisions of materials in an illustrative form of too-th.

Fig. 13 represents diagrammatically an illustra tive form of actuating device or means for securing relative motion of the piston and assembled mold, with an auxiliary means for securing transverse compression of the mold during the comu pressing `actuation 0f the piston.

Before discussing the mold construction in de. tail, the molded article with the varying requirements thereof, as disclosed in Fig. 12, will first be discussed and the parts identified so that the explanation to follow will be more readily understood. Referring to this gure, therefor, a lower mold portion or piece l@ is provided containing the upwardly presenting recesses ll, and the upper mold piece l2 contains the downwardly lpresenting recesses I3 and the registering recesses dei-lne `a complete closed mold cavity lll the only opening into which aside from possible flash through the parting line l5 is the sprue channel I6. The mold cavity is rst charged with a chosen lot of mate-l rialpreferably of more or less translucent nature, as at il, which not only forms the incisal tip portion substantially symmetrically disposed on both sides of the parting line l5, but also, as shown at iS lies along the surface of the lower recess H to form in part at least the 1abial`sur face of the finished tooth. To this end it will be understood that the dispositionfof the powder` il and I8 so lthat it assumes theshape shownvwill prefelably be ,accomplished by subjecting the powder to both centrifugal force Imoving toward ,the -incisal tip, and also to the action `of gravity urging the powder .to cover the Vlower recess I I. The illustrative preliminary plastic assembly fur.- ther comprises a ,charge of a contrasting mate.- rial Z, comporting with the visual aspect of enamel of a vital tooth, and which may be more or less .symmetrically disposed in the mold cavity -I between the labial layer I-B ,of .the incisal material il, andthe surface of recess I3. If found desirable still a third material in powdered form 2| may the provided of still further contrast to `the incisal tip I'I as well vas ,to enamel portion 20. It will he understood that after completion of the molding, the finished molded plastic tooth will have components occupying the same relative positions therein as those .disclosed in the mold as a preliminary to actual molding.

Referring now to the .earlier figures, it will be seen thatI .the mold comprises a lower preferably cylindrical piece Ill, preferably made of metal both for longevity and for rapid 4heat conduction although any other material may he used. The lower mold .piece I is provided in its upper surf face A22 with a plurality of independent mold recesses ,H each extending generally radially of the center of the piece, and Iall `being disposed in an annular series substantially concentric of the said center of the piece. The upper mol-d piece I2 has a plurality of the independent mold recesses I3 formed in its lower face 23, .each extending generally radially of the cen-ter of the upper piece and also arranged in an annular series concentric with such center, and each respectively arranged for juxtaposition with a complemental lower recess H. The upper cylindrical mold piece I2, preferably, in its lower surface 23 has fa plurality of incomplete downwardly presenting channels 24 vforming with the contiguous surface 22 of lower mold piece ill, the sprue .channels I6, which extend `generally radially of the upper mold piece in communication with lthe respective mold recesses I 3 at one vend and with a -generally axially extending central bore 25, forming vthe hopper or reservoirfor the assembled mold. This `latter is of :appreciable size so as to receive a large piston to be .described and so as to permit a feeding tube to be adjusted angularly therein, Aas, will also be described. It will be .understood that the sprue channels can also be formed in the upwardly lpref senting face 22 of the'lower piece I0, or they may be formed in both pieces for registration to complete .the channels. An important feature lies in the utilization of mold cavities of different sizes or volumetric capacities, in .connection with which it is preferred to vary the effective areas or Widths of Ithe associated sprue channels, so as to proportion the inflow of Vmolding material tothe inold cavity in which itis to be disposed.

IIt will be 'understood that suitable anchoring means, such as the pin .and recess combinations shown :at 2B and 2l, respectively, will be provided, to prevent relative angular motion of the upper andzlower cylindrical mold pants, and also suitable means such as axial recesses (not shown) will be provided .if necessary to enable the Iassembled mold -pieces to be anchored upon a spinnable table 29.

vIn charging, the mold as thus described, in what may be vdesigna-ted as one desirable form, will bear-ranged for generally `centrifugal charge ing ,of the vmold cavities, with an Aattendant utili.- zatipn of the force .of gravity to secure a resultant force .effective upon the powder charge. To this end the spinning table 2S will be susceptible to control and be selectively variable in its speed to secure the proper combinations or the proper line of resultant forces on the powder masses. With the mold on such table, the tube 30 will be disposed so that its upper end is in a feeding trough or iirst hopper or in communication with some source for delivering an amount of incisal material il that when properly distributed will just fill the incisal tip and provide for a covering of the labial surface of the teeth in all of the respective mold cavities I4. If the tube 30 delivers this amount to the charging hopper 25 adjacent to the inner ends of the spru channels IB, spinning the table at a properly coordinated speed will cause the powder to be flung outwardly through the sprue channels into the respective mold cavities, in which latter it Will be caused to assume the position indicated at Il and I 8 of Fig. 12. If thereafter, a second charge of the powder were carefully metered into the tube 30 to provide just enough enamel material to furnish enamel 20 to all of the mold cavities I4, it Would be fed through the sprue channels I6 and be compacted against the material for the incisal tip I'I, and against the extension I8 thereof, and if desired the rate of delivery of this material or the centrifugal force available upon it could be varied relative lto that used on the material I1 if desired, so as to urge it to more or less symmetrical disposition in the mold cavity, according to the necessities of the particular case. If after the second charge has been disposed in the respective mold cavities in the manner just described, the tube was then supplied with a third charge, say of material 2|, it will be clear that thereupon after delivery to the hopper reservoir 25, the mold cavity could be completely filled. Thereafter, by a continuation of material 2l, or with care after the mold cavities were properly filled, with still another material, possibly com# prising scrap or waste material or material discarded from other processes or techniques being practiced, the sp1-ue channels I6 would be lled, and thereafter the hopper reservoir 25 would be filled, preferably, almost to the top, and the charging would then be complete.

It will be clear that with the step by step intermittent charging thus described, there would be both a careful proportioning and Aalso a careful relative shaping of the components, but it will also be clear that under such charging circumstances the line of demarcation between contiguous charges will be abrupt. I n some cases this may be preferred. However, in other cases a more subtle and delicate demarcation, marking by blending of one into the other, maybe preferred, as it almost certainly will with teeth as the article molded. In this'case it will be clear that there are several ways of accomplishing the result. For instance it will be clear that the delivery into the pipe or tube 30 may be progressively a shutting down of the rst metered charge with a gradual beginning of the second metered charge, and so forth, so that there is a portion of the delivery which includes particles from both charges which forms the blending layer leading into the respective different materials. In the alternative, perhaps, would be the provision of additional pipes 3Q so that in overlapping relation one, two or more pipes or tubes could be delivering their contents simultaneously to the charging hopper 25, for part of the 'charging operation.

In this preferred type of charging it Will be clear that the tube'can deliver its flowing stream of pulverulent material to the center of the hopper, or eccentrically thereof just at the hopper and mouth of the sprue channels. Preferably, as noted, the cross-sectional area or width of the respective sprue channels will vary to accord with the varying volumetric capacities of the respective associated mold cavities so as to properly proportion the inow of shaded molding material to the respective mold cavities. A still further modification of the powder feeding tube 30 is having its main part concentrically arranged, but having its delivery mouth off-set therefrom Within the hopper chamber 25, and arranged to be rotated, so that while delivering themain ltube is rotated on an axis concentric with the mold, while the delivery mouth' thereof delivers the owing stream successivelyto themouths of the respective sprue channels as they are passed in the relative rotation of the parts. It will be understood that in this form of" discharge for the charging powder, tube 30 may berotated, the mold may be rotated, or they may both rotate in opposite directions or differentially in the' same direction. l

In the form of invention shown in Fig. 10, which in many cases may be preferred, the mold in all of its details is similar to that of the preferred form except that a cone 3| may be formed in the lower mold piece and the sprue channels 'i tion it will be clear that'the movable delivery f" tube will enable proper and uniform charging of the mold cavities. Again the sprue channels are preferably predetermined in width to admit the proper proportion of shaded charge according to mold cavity capacity. y

In every case of charging it will be clear that the mold cavities are lled with a-Compact mass of powder with no appreciable voids other than those inherent inthe use of the particular granules used.

The molding operation. With a given mold charged to the degree indicated in the preceding discussion, and with the hopper reservoir preferably almost completely lled, it is then -subjected to heat in any desired manner topartially polymerize or plasticize the entire column of powder in the mold cavities, sprue channels and charging reservoir. This can be expeditiously accomplished by placing the assembled charged mold upon a suitably heated plate 39, (Fig. 6), or placed in a flame, or in an induction heater or the like, so that a given time cycle of heat is undertaken.

This timed heat exposure converts the dry powder into an extremely viscous deformable mass of the consistency perhaps of slowly workable putty assuming a molding material such as polyvmer of methyl methacrylate for a purely illustrative example. Obviously the entire mass from one end of the mold cavities: through the sprue channels, and into the hopper is a uniform plasticinelastically deformable or compressible unit. The heating time is carefully arranged inv accordance with the masses of metal to be considered as present in each mold, if this comprises the material of the mold pieces to the end that the heating cycle is substantially identical 'for all molds of a series.

At the end lof the heating cycle, vwhich may comprise for instance five minutes', the heated 10 mold is subjected to the action of the pressure plate 32 having a lower planar surface 33 or is otherwise held together tightly to preclude separation and minimize flash during molding as for instance by hydraulic or other device 59, of Fig. 13. While maintaining flash minimizing pressure the piston 35 is forced axially downwardly upon the more or less deformable mass in the hopper 25, illustrated in Figs. '7 and 8, as by ahydraulic or the like cylinder liti, shown in Fig'. 13. The mold cavity pressure produced by the piston must be less than the pressure exerted by pressure plate 32. The pressure exerted by the piston on the powder in the mold cavities fuses and/or solidifies and/or polymerizes the entire column of plastic in the mold cavities and sprue channels. This is facilitated by rapidly chilling all of the parts while maintaining both plate and piston pressure. In some cases there may be a very thin flash d3 formed betweenl the mold halves joining the molded articles i2 as indicated in Fig. 9, but this is usually of no moment and in many cases will be non-existent. To this lend it is only necessary to have properly complemental meeting faces for the parts and to make certain that the pressure from plate 32 on the mold halves in assembled relation is of a value greater than that in the mold cavities produced by piston 35.

It will be clear that the mold is readily disassembled and the completely molded article easily stripped off, and the articles easily stripped from the waste gates and sprues.

An illustration of a molded article has been given but it will be clearly evident that other and different articles can be molded by the molds and processes disclosed herein. Thus it will be clear that a single shaded charge may be used if an article of a single uniform visual aspect is desired. It will also be clear that in charging the molds it is not necessary that all charging particles enter the mold units through the sprue channels, as some parts might be placed in given mold recesses before they are closed by the complemental mold piece and thereafter the charging mixtures thereof with materials which cannot the reservoir bore, subjecting the powdered plastic material in the reservoir bore to force to transfer. it from the reservoir bore through the passage and into the mold cavity, continuing the force while continuing the feeding to the reservoir bore untilaa compact column of powdered plastic molding material is disposed in the mold cavity and passage, feeding additional plastic material to the reservoir bore to form a termination for said column in the reservoir bore, plasticizing the oo'lumnof molding material, then subjecting ther slestczed, material irl the molti cavity to momias ,pressures by Compression. gf the materiallathe reservar bor@ by forte Separate and ntiepellsl et. ofthe force for transferringthef-unplastlcized material into they mld eavity 2, AIn molding articialteeth with at least two visually contrasting predetermined portions in a mold cavity of a mold having a charging reservoir bore and a sprue channel communicating with the mold cavity and bores-the method which comprises passing plastic material Which-is tojforni one predetermined portion of such tooth into the charging reservoir bore, transferring said plastic material bv force from the reservoir here into the moldear/ity through said sprue channel, disi posing the said material properly in the mold cavity to cause it to bek properly shaped therein hysaid force, continuing to introduce plastic inaterial into said reservoir bore and continuing the transfer of said plastic material. into the incid cavity by said force from, said reservoir` `bore through the spruechannel while changing from one material tol the second Visually contrasting material, continuing to shape the materialin the rrioldv cavity by` said force vvhile continuing; the charging of the mold cavity with said second' ma. terial alone, thus blending the materials, continuing to pass plastic molding material intorthe reservoir and transferring it by 'said force into the sprue channel and continuing to pass plastic molding material. into said reservoir to form a mass` of plastic material which is continuous from the mold cavity through the sprue channel and into the reservoir bore, heating the entire-column of plastic material in situin the mold cavity sprue channel and reservoir to plasticize it for subsequent molding by compression, and nally molding the plasticized column by 4compressing the plasticized material in thereservoir boreby force independent andv 'separate 'from the force used for said transfers.

3. ',Inn'iol'ding artificial teeth With at least. two visually contrasting predetermined portions' utilizing a mold including a reservoir, aA sprue chantnel and a mold cavity, the methodv'vhich comprises passing a rst plastic material into 4said reservoir', transferring the 'rsti plastic 'Iiiai'feliall by force from the reservoirmthroughthe"sp'r,ue channel into'the moid cavity and' by the samef force shaping the material in the mold Cavity 4SQl as to define substantially the predetermined pro,- portions and visual aspect of one portion vof the ultimate molded tooth, then passing' a second plastic material into' the reservoir, transferring' the second material from the reservoir by thel same force through the sprue channel into the moldY cavity to impart to the ultimate molded tooth the predetermined proportions and'visual' aspect desired relative to the irst material-,- in a compact body of plasticmolding material in the mold cavity, heating the compact body of plastic molding material Ain situ in the mold cavity to plasticize andto condition it fori molding by compression, and subjecting the plasticized body'in the mold cavityto compressive force separate'and` independent from the said transfer force.

4. In molding, the method of charging a closedl mold cavity having a sprue channel and a bore reservoir, with visually contrasting materials, which comprises introducing material to the mouth ofthe sprue channel in the bore, 'subjecting the material to centrifugal force such as; toV position the material in the proper portionsv of the mold cavity to establish one`propQrtioriateI part of the iinished article, introducingvisually contrasting material to the mouth of the sprue;

the here and subjecting it to centrifusal ist-Cs ailettes t9: dispose l t ill-,the mold. Cavity ift wpst-ppertiogalrelatl, in the finished 4 filling ttl@ Seite channel. With molding mgttrlat matias the meld ,to plastici@ the @ntl-re mass ouf/,m2o ing material, and molding by subf Cl mass in the br torressure'in a lline tra Ve'se of the centrifugal force. m. In molding, thernethod of charging a closed y A 'having 'a sprue channel and a bore reserVoir.; With visually contrasting materials, which comprises introducing one material to the mouth Qi the spruefcliaiinel in the bore, subject.-

' teria'l to force such as` to position the `ting, material 'alonso as to disposeisame in contacting relation to thev blending material, introducing mQldine materia-1 to the @"tllllll'til inthe bore and Subsubject said incisal tip material to' centrifugal force such as to noveiitt-ipt the'rnld- `cavity to dispose it'irithe 'in s al'tip as Welifa'sl to dispose it-f'orthe form'ationofpart atleast of the, labial Surfci'fysl 'ttli bldg `the irlisal tip material into enamel material of contrasting visual 'aspect andiiritrolucing'tlie blended mater-ils''te *thiuthmff thespre channel While continuing 'the rotation fo'fftn' rmoicito move'the blended iratrialsthroughfthesprue channel into the meld'eayityby subjecting" it to centrifugal force to 'a'us'ei it tooverli'e the' previously disposed iicisagl'-tip'niateriall;tvhilestill continuing the rottiiiof'tlie moldintrducing enamel material toftti'e'moutlil 'of-the spru channel' and subjecting it`to cehtifugfallfoifcsuch asto cause it tochter tne'mbia'tavty anabefsna'ped therein to-compact. behi-rclltheincisalftip and blendedmaterial in the incisal tip and also along the labial face, continning the rotation of ythemoldvvhile introducing moldingfma'teifial tothemuth of the spruechann'eiaiatmoifing' it into theisprue channel by cen'.- trifugal' force, charging the' reservoir with molding'atrial, plasticizingthe materialinzthe mold cavity spine-channellandreservoir so as to render4 ity susceptible to. moldinefbypressure, and subjecting-tha pllasticizedv massief-*molding material tomoldig; pressures .bycompressing-the material in thelbore in ay direction: transverse of the centrlfusal'force.

l?. Theimethodef, Charging@ mcldwvitv for teeth: havingy inc' l-ftp: and-Which is. Closed except-far ai smug, channel satema. the mal@ cavity remote from the incisa] tip molding pore tontliereet aadwhithllas a reservoir bore in cpmmunicationwth Such aprile channel, which 13.. comprises disposing at the mouth of the sprue channel a succession of plastic materials of visually contrasting nature, in continuously subjecting the materials to centrifugal force to cause them to pass through the sprue channel and into the mold cavity and to cause them to be shaped and proportioned in the mold cavity, the plastic materials passing gradually from incisal tip material tc enamel material during maintenance of the force, and said force being effective to compact the successive shaped materials in the mold cavity and sprue channel, charging the bore reservoir with molding material, heating the compacted and shaped material until it becomes responsive to compression for molding, then compressing the entire mass of heated material.

8. The method of molding an artificial tooth in a two part mold having a mold cavity having a sprue channel as its only entrance and with a charging reservoir, which consists in charging the reservoir with molding material, by centrifugal force charging the mold cavity and shaping therein successive visually contrasting materials from the charge in the reservoir by centrifugal -force, in charging the sprue channel and at least partially additionally charging the reservoir to form a more or less continuous column of molding material from the mold cavity through the sprue channel into the reservoir, heating the column of material until it becomes responsive to compression, compressing the entire column by pressure in the reservoir and maintaining the pressure while permitting the column to cool.

9. The method of molding an artificial tooth which comprises charging a column of molding material from a reservoir by passing it by centrifugal force through a sprue into a two piece mold having a mold cavity having a parting between the two pieces of said mold, disposing material in the mold cavity by centrifugal force to establish at least two visually contrasting portions, heating the material of the column to render it capable of consolidation under pressure, pressing the two pieces together to reduce flash at the parting, and while maintaining ilashreducing pressure subjecting the entire column to a solidifying pressure in the reservoir separate and independent of the pressure exerted by centrifugal force and maintaining the said separate and independent pressure while the column cools, then separating the mold and stripping the molded column and teeth from the mold, then separating the teeth. K

l0. In molding in a separable mold defining a mold cavity a sprue channel and a reservoir, the method of molding which consists in feeding relatively uncompacted dry powdered plastic molding material to the reservoir, in subjecting the material in the reservoir toa force to cause it to pass from the reservoir through the sprue channel and into the mold cavity, in continuing the feeding while maintaining the force until the mold cavity and sprue channel are vfilled. with relatively compacted dry powder, heating the compact dry powder in the mold cavity sprue channel and reservoir in situ to plasticize same to render it susceptible to molding by compression, and molding the plasticized mass by pressure thereon separate and independent from the said force.

li. The method of molding utilizing a mold provided with sprue channels and molding cavities in which the charging reservoir communicates with the mold cavities by means of sprue channels, which comprises feeding dry thermoplastic molding material in powdered form to the charging reservoir, subjecting the mold to rotaaisne@ 14 tion to develop centrifugal force on the dry powder to cause some of it to pass laterally out of the reservoir through the sprue channels and into mold cavities and to be compacted in columnar form in the mold cavities and sprue channels,

heating the mold to transform the dry powder into a partially plasticized mass in columnar form terminating in the reservoir, and exerting pressure on the terminal portion of the mass in the reservoir in a direction substantially at right angles to the direction of the centrifugal force to compress the plastic mass in the mold.

12. The method of molding artificial teeth in a separable mold having a plurality of tooth mold cavities of relatively different volumetric capacities and proportionate effective entrance sizes to form teeth of relatively different sizes each having two visually contrasted predetermined portions which are proportionately similar in teeth of relatively different sizes, which comprises feeding two successive visually relatively different charges of dry powdered molding material to the entrances to the respective mold cavities, moving the particles of the charges successively to the mold cavities and shaping them therein by mechanical force while automatically varying the rate of inflow to the respective mold cavities to proportion the respectively visually different charges in the respective mold cavities of the plurality to fill the respective mold cavities.

' 13. The method of molding artificial teeth in a separable mold having a pair of mold cavities of respectively different mold capacities with sprue channels of respectively differenty effective widths leading from a common reservoir to the respective cavities in order to form teeth of relatively different sizes each having a plurality of visually contrasted predetermined portions which are proportionately similar in teeth of said relatively different sizes, which comprises feeding plastic molding material to the reservoir adjacent the mouths of the respective sprue channels in a plurality of successive visually contrasting charges, passing respectively different amounts of each successive charge of molding material by force from the reservoir to the respective mold cavities predetermined by the different eective widths of the associated sprue channels, and shaping the respective predetermined amounts in the respective mold cavities by the same force.

14. The method of molding in a separable mold having a pair of mold cavities of respectively different mold capacities with sprue channels of respectively different effective widths leading from a common reservoir to the respective cavities, which comprises feeding molding material to the reservoir adjacent the mouths of the respective sprue channels, passing a predeterminedly different amount of molding material by centrifugal force from the reservoir to each of the respective mold cavities, shaping the respective predetermined amounts in the Yrespective mold mouths of the sprue channels Iin the reservoir, and filling the sprue channels therewith by@V4 `the respective mold cavities. l

22. `A separable mold for artificial teeth comaes/telit* prising a mold formed of a plurality of pieces, means dening in the mold a pair of mold cavities of which one has a greater volumetric capacity than theother to form a larger shaded tooth than is formed in said other, a common charging reservoir, sprue channels in communication with and extending generally radially ofthe charging reservoir and in communication with the respec-` tive mold cavities of the pair, the respective sprue channels having different eiiective Widths so as to predeterminedly proportion shaded material passing through the sprue channels from the reservoir to the respective mold cavities, means for depositing successive charges of respectively differently shaded molding material in the reservoir in position to pass through the respective sprue channels in respectively proportioned amounts, and means for rotating the mold to cause material in the common charging reser voir to pass through the respective sprue channels and to proportion material in the respective mold cavities.

23. A molding apparatus for molding plastic material into artificial teeth comprising a plurality of separate mold pieces arranged in assembly to form a mold having a compression reservoir bore, a plurality of tooth mold cavities spaced from the bore and a plurality of sprue channels extending respectively between the bore and the respective mold cavities, a piston arranged for relative movement into and for compressing action in said bore and for relative withdrawal from said bore in the assembled condition of said mold, said bore being arranged to receive plastic molding material, means for rotating the mold in assembly to subject the material in the bore to centrifugal force to urge molding material through the sprue channels and into the mold cavities to form closely compacted columnsfof material extending from the mold cavities through the sprue channels and to termination in a mass of molding material in the bore While maintaining the mold in assembly, means for plasticizing the material of the said compacted columns while the mold remains in assembly to condition the material for final molding by pres.

sure, and means for relatively moving the piston and bore of the mold in assembly to compress the mass within the bore and thus to subject the plasticized columns in the sprue channels and mold cavities to molding pressures.

24. A molding apparatus for molding plastic material into articial teeth comprising a plurality of separate mold pieces arranged in assembly to form a mold having a compression reservoir bore, a plurality of tooth mold cavities spaced from the bore and a plurality of sprue channels extending respectively between the bore and the respective mold cavities, a piston arranged for relative movement into and for compressing action in said bore and for relative Withdrawal from said bore in the assembled condition of said mold, said bore being arranged to receive plastic molding material, means for rotating the mold in assembly to subject molding material in the bore to centrifugal force to urge molding material through the sprue channels and into the mold cavities to form closely compacted columns of material extending from the mold cavities through the sprue channels and to termination in a mass of molding material in the bore while '18 maintaining the*v moldin assembly, means for plasticizing the material of the said compacted columns while the mold remains in assembly to condition the material for nal molding by pressure, means for subjecting the mold in assembly to pressure to prevent separation thereof during .application of pressure upon the plasticized columns, and means for relatively moving the piston and bore of the mold in assembly to com-l press the mass within the bore and thus to subje'ct the plasticized columns in the sprue channels and mold cavities to molding pressures while still maintaining the mold in assembly and during the maintenance of said separating-preventing pressure thereon.

25. A molding apparatus for molding plastic material into artificial teeth comprising a plurality of separate mold pieces arranged in assembly to form a mold having a compression reservoir bore, a plurality of tooth mold cavities spaced from the bore and a plurality of sprue channels extending respectively between the bore and the respective mold cavities, the upwardly presenting portions of the respective mold cavities forming the labial surfaces and the surfaces of the respective mold cavities remote from the bore forming the incisal portions of the ultimate respective molded teeth, a piston arranged for relative movement into and for compressing action in said bore in the mold in assembly, means for charging the bore with incisal tip plastic molding material in the mold in assembly, means for rotating the mold in assembly at selective speeds to subject the material with which the bore is charged to substantially predetermined centrifugal force whereby the incisal tip material is urged through the sprue channels and into the mold cavities in which it is disposed adjacent to the mold surface forming the incisal surfaces and partially at least by gravity upon the mold surface forming the labial surfaces of said mold cavities, said molding means also being arranged'` to charge the bore with differently shaded plastic material, said rotative means being arranged to subject the last mentioned shaded material to substantially predetermined centrifugal force to cause the last mentioned plastic material to pass through the sprue channels and into the mold cavities to disposition behind the material at the incisal tip and to overlie the incisal tip material on the labial surfaces of the said mold cavities by gravity while maintaining the mold in assembly, said charging means also being arranged to charge the bore with additional amounts of plastic molding material, the rotative means being operable to develop substantially predetermined centrifugal force to cause the plastic material in the bore to pass by centrifugal force into and to complete the filling of the mold cavities and to fill the sprue channels by centrifugal force to form closely compacted columns of molding material extending from the incisal surfaces of the mold cavities through the sprue channels to termination in a mass in the bore, means for plasticizing the entire mass of material, and means for relatively moving the piston and the bore of the mold in assembly to compress the mass in the bore and thus to subject the plasticized columns to molding pressures While still maintaining the mold in assembly.

FRED A. SLACK, JI'.

(References on following page) :is REFERENCES y'CITED 29 'FOHEIG PATENTS Dif.v 3, page v255.

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